"Katie and Yigal have been together for a while," says an insider. "She goes everywhere with him. He's into brunettes, and Katie is his right-hand woman. They're so close that Yigal even watches Katie's dogs when she's away."

Not helping is Joel's constant touring, and the fact that the duo
lead very separate lives.

"Katie often stays at their apartment in New York City alone, while Billy likes to live in their Long Island home," another source tells us. "They're rarely together. And Katie likes it like that. She wants her freedom."

When the "Piano Man" originally heard of the "fashion designer" friend, he assumed the Israeli-born Azrouel was gay, according to "The National Enquirer." Not so.

The ex-military man has "slept with several high-profile female fashion editors. It's understandable that everyone would think he's gay, as he's a man of fashion in New York City, but he isn't," says the source.

Meanwhile, an insider told "The Enquirer": "Initially, Billy thought it was great that she met a new friend. But now he's become very concerned."

He may have reason to be. At a recent Museum of Natural History gala, Katie turned up, sans Billy, and spent the evening with Yigal. "I love Yigal Azrouel," she told us that night. "He's one of my favorite [designers]. We're good friends. He's very easygoing."

A week before that, the two left a USA Network's party just a few minutes apart from one another. Katie wasn't wearing her wedding ring, and jumped into a waiting cab that Yigal was already in, said an onlooker.

Sounds like Billy should dust off one of his old tunes to help him cope. We recommend "A Matter of Trust."

"Piano Man" Billy Joel hit a high note for a group of East Harlem music students, donating an autographed Steinway baby grand for auction to help raise money for their lesson program.

The $60,000 piano will be sold on CharityBuzz. com, where bidding began last week and will continue until May 6th, 2009.

"I feel good because I really want to continue violin in the future," said Satouma Viallo, 12, one of about 20 students at Mount Carmel-Holy Rosary School in Manhattan.

"Whenever I feel sad or lonely, I just pick up my violin and I feel better."

The young musicians now spend three hours on Saturdays studying music through Ten O'Clock Classics, a nonprofit that provides free lessons and instruments to Catholic-school children.

Joel is a board member of Ten O'Clock Classics.

Auction proceeds will add hours of classes next year that will include music theory, ear training and possibly individual lessons, said the group's founder, Ronen Segev.

Ten O'Clock's chairman, real estate developer David Picket, said he'll put up any extra money needed to make it happen.

Many of the Mount Carmel youngsters have their hearts set on auditioning next month for the Music Advancement Program (MAP) at the vaunted Juilliard School at Lincoln Center.

Started in 1990 and aimed at underprivileged kids, MAP typically accepts 40 to 50 new students each year. Most pay only a fraction of the $4,500 tuition.

Last year, Mount Carmel seventh-grader Bianca Odle, 12, was put on the program's waiting list.

"I was disappointed and angry, because I thought this year would be my chance," she said.

The Broad Foundation pledged $425,000 to MAP over four years, said Juilliard School President Joseph William Polisi.

"The seven-figure gifts that were not abnormal two years ago are very abnormal now," Polisi said.

Proceeds from the sale of Joel's piano should allow Ten O'Clock Classics to give Mount Carmel's budding musicians the training they need to make MAP, Segev said.

"When people see that these children who are facing many challenges are so focused and positive and determined," Segev said, "It really strikes a chord with them."